Update serious_python dependency to version 0.9.4

Replaces the git-based override for serious_python with the published version 0.9.4 in pubspec.yaml. The previous git reference is now commented out for reference.

{{cookiecutter.out_dir}}/pubspec.yaml

@@ -29,11 +29,13 @@ dependency_overrides:
   #     ref: feodor/flet-0-27-5-fixes
   #     url: https://github.com/flet-dev/flet.git
 
-  serious_python:
-    git:
-      url: https://github.com/flet-dev/serious-python.git
-      ref: main
-      path: src/serious_python
+  serious_python: 0.9.4
+
+  # serious_python:
+  #   git:
+  #     url: https://github.com/flet-dev/serious-python.git
+  #     ref: main
+  #     path: src/serious_python
 
   wakelock_plus: ^1.2.10
   web: ^1.0.0